More than 35,000 motorists have joined a class action lawsuit against VW in England and Wales over the emissions scandal.

The size of the group is increasing at the rate of 500 drivers a day and lawyers are confident the legal action will eventually involve about 100,000 owners of VW, Audi, Skoda and Seat cars.

Damon Parker, of the law firm Harcus Sinclair, said the action began with a small number of individuals coming forward. “They came to us with concerns that they had bought these cars which they thought were of a certain quality, which they thought were less harmful to the environment.

“They said they would never have bought them if they had known they were not of satisfactory quality. From a few people coming to us it has just grown. We set up a call centre in our basement and employed 20 extra people to take calls.”

The action is seeking compensation from VW for selling cars that the lawyers argue were not road worthy because the emissions were far higher than they purported to be.

This month, the carmaker pleaded guilty to all criminal charges in the US, admitting to a scheme to sidestep pollution rules on nearly 600,000 vehicles. VW admitted conspiracy and obstruction of justice in the scheme, which used software called a “defeat device” to suppress emissions of nitrogen oxide during tests.

The firm has agreed to pay $4.3bn (£3.5bn) in civil and criminal penalties in the US. But in the UK the government has not taken the carmaker to court over the scandal.

Lawyers in the UK action will claim British drivers should be compensated because they paid more for what they thought were clean diesel cars. Each motorist is seeking thousands of pounds in compensation.

Liz Gabrel, the owner of a VW Tiguan, was one of the first to join the legal action. “I felt strongly about joining the VW emission action group because VW have shown total disregard for the environment and their customers,” she said. “It would not be right for VW to get away with such poor behaviour and with the court action they will be answerable in the public arena.”

Harcus Sinclair alleges that the diesel cars emitted far higher levels of NOx – a mixture of nitrogen oxide and nitrogen dioxide – than stated. “It is clear to us that the vehicles were fitted with ‘defeat devices’ which allowed them to appear to pass emissions tests; and … the vehicles did not (and do not) meet the regulatory requirements necessary to register and sell a car in the UK, because the levels of NOx emitted are considered to be dangerous to public health.”

Mary Creagh, the Labour chair of the Commons environmental audit committee, said the government should take VW to court.

“Almost a year and a half on, the government has taken no action against VW for deliberately fitting cheat devices on their cars to fool regulators,” she said. “Given the UK government’s inertia, it is inevitable that motorists are taking matters into their own hands and pursuing private action in the courts.

“The environmental audit committee has called on government to measure the contribution that Volkswagen’s cheat devices made to meeting UK emissions standards, and use the results to pursue court action in the UK.”

John Hayes, the transport minister, has promised to support the legal action being taken by consumers.

Harcus Sinclair is collaborating with other law firms who have clients taking action against VW. The case is due in the high court in May.

VW was contacted for a comment but did not respond.

The firm has recalled 1.2m cars in the UK but the head of VW UK, Paul Willis, told MPs at a recent select committee hearing that no cars in Europe had been affected by defeat devices installed in the vehicles. He also denied misleading or deceiving customers in the UK.

VW is carrying out “technical fixes” at the rate of 20,000 a week in the UK. It also owes the government £1m for the cost of testing the Department for Transport had to carry out when the scandal emerged.

In 2015 the US Environmental Protection Agency said 482,000 VW-built cars had been fitted with software that detected when the vehicles were undergoing official emissions testing and switched the engines to a cleaner mode. The company later admitted that 11m vehicles worldwide were fitted with the software.